Ostarine or RAD-140: What Is the Difference

Ostarine (enobosarm, MK-2866) and RAD-140 (testolone) are two of the most popular selective androgen receptor modulators (SARMs). They are often compared by "strength," but something else is much more important: how much is known about each of them from clinical trials and what is known about their risks. The editorial team examines the difference between these substances from the standpoint of evidence-based pharmacology.

What SARMs are and why they are not "safe steroids"

SARMs are non-steroidal molecules that bind to the androgen receptor and, by their developers' intent, were supposed to act mainly on muscles and bones, affecting the prostate, skin, and other androgen-dependent tissues to a lesser extent. This idea of tissue selectivity is described in detail in a review by Narayanan, Coss, and Dalton (2018).

SARMs were developed for the treatment of sarcopenia, cancer cachexia, osteoporosis, and certain types of breast cancer. However, as of today no SARM has been registered as a medicine by either the FDA or the EMA.

Tissue selectivity is a relative concept. In clinical trials SARMs still lowered one's own testosterone levels and affected lipids, and in the real world reports of drug-induced liver injury have appeared. So the label "safe alternative to steroids" has no scientific basis.

Both substances in question are included in section S1.2 "Other anabolic agents" of the WADA Prohibited List and are prohibited for athletes at all times.

Ostarine: the most studied SARM

Ostarine (GTx-024, enobosarm) belongs to the arylpropionamide SARMs. It is one of the few substances of this class to have undergone randomized clinical trials with published results.

In a placebo-controlled phase II study (Dalton et al., 2011), healthy elderly men and postmenopausal women received ostarine for 12 weeks. In the 3 mg per day group, a statistically significant increase in lean body mass and improvement in a physical function measure (stair climbing) were recorded compared with placebo.

Enobosarm was then studied in phase III (the POWER program) in patients with non-small cell lung cancer and cachexia. The design of these studies was published in 2016; according to available reports, the drug did not receive regulatory registration based on these results.

Later enobosarm was also studied in androgen-receptor-positive breast cancer. That is, ostarine has the broadest clinical history among SARMs, but it concerns specific patient groups and does not make it an approved medicine.

RAD-140: strong in preclinical work, little human data

RAD-140 was developed by Radius Health. Its preclinical characterization was published by Miller and colleagues (2011): in animal models, in particular in experiments on primates, the substance demonstrated a pronounced anabolic effect on muscle tissue with a relatively smaller effect on the prostate.

In humans RAD-140 was studied mainly in early phase I trials in women with hormone-receptor-positive metastatic breast cancer, where safety and tolerability were assessed. There are no large randomized trials in healthy people.

Instead, clinical cases of drug-induced liver injury have appeared in the medical literature in people who took products with RAD-140, for example reports by Flores and colleagues (2020) and Barbara and colleagues (2020).

Thus, the high "strength" of RAD-140 that sellers write about rests on preclinical data, not on controlled studies in humans. For safety assessment this is a fundamental difference.

Comparison by evidence base

The main difference is not in "strength" but in the volume of knowledge. For ostarine the effects at specific doses in certain groups of people over a limited time are known. For RAD-140 such knowledge is mostly absent.

At the same time, even the data on ostarine do not describe long-term use or combinations with other substances, so they cannot be transferred to the practice of amateur athletes.

Risks: liver, lipids, hormones, quality

A review by Solomon and colleagues (2019) summarizes that in clinical trials of SARMs a decrease in HDL and suppression of one's own hormones were observed. As with other androgen receptor agonists, this is natural: the pituitary "sees" an androgenic signal and reduces the production of LH and FSH.

• Liver:cases of cholestatic and mixed injury have been described with the use of products containing ostarine, RAD-140, and other SARMs.
• Lipids:a decrease in HDL is one of the most consistent effects of the class.
• Hormones:suppression of testosterone, LH, and FSH; a possible effect on fertility.
• Uncertainty:the absence of data on long-term use.

A separate problem is product quality. A study by Van Wagoner and colleagues (2017) in JAMA analyzed products sold online as SARMs: only about half of them contained precisely the substance that was declared, some contained other undeclared substances, and the amount of active substance often did not match the label.

The FDA has repeatedly warned consumers about products with SARMs, noting risks to the liver and cardiovascular system.

Editorial conclusions

Ostarine and RAD-140 are non-steroidal androgen receptor modulators of different chemical structure. Ostarine underwent clinical trials up to phase III, RAD-140 only early studies in oncology patients.

Both substances are not registered as medicines, suppress one's own hormones, affect lipids, and are associated with cases of liver injury.

Products with the name SARM on the market often do not match the label, which makes risk assessment even more difficult.

We also recommend reading "Ostarine vs RAD-140: what to choose and for whom," an article about what SARMs are, and a review of liver tests in athletes.

References

1. Dalton JT, Barnette KG, Bohl CE, et al. The selective androgen receptor modulator GTx-024 (enobosarm) improves lean body mass and physical function in healthy elderly men and postmenopausal women: results of a double-blind, placebo-controlled phase II trial. J Cachexia Sarcopenia Muscle. 2011;2(3):153–161.
2. Miller CP, Shomali M, Lyttle CR, et al. Design, synthesis, and preclinical characterization of the selective androgen receptor modulator (SARM) RAD140. ACS Med Chem Lett. 2011;2(2):124–129.
3. Narayanan R, Coss CC, Dalton JT. Development of selective androgen receptor modulators (SARMs). Mol Cell Endocrinol. 2018;465:134–142.
4. Solomon ZJ, Mirabal JR, Mazur DJ, et al. Selective androgen receptor modulators: current knowledge and clinical applications. Sex Med Rev. 2019;7(1):84–94.
5. Van Wagoner RM, Eichner A, Bhasin S, et al. Chemical composition and labeling of substances marketed as selective androgen receptor modulators and sold via the internet. JAMA. 2017;318(20):2004–2010.
6. Flores JE, Chitturi S, Walker S. Drug-induced liver injury by selective androgenic receptor modulators. Hepatol Commun. 2020;4(3):450–452.
7. Barbara M, Dhingra S, Mindikoglu AL. Drug-induced liver injury associated with Alpha Bolic (RAD-140) and Alpha Elite (RAD-140 and LGD-4033). ACG Case Rep J. 2020;7(6):e00409.
8. World Anti-Doping Agency. International Standard: Prohibited List. Montreal: WADA; 2025.